Continuous non-invasive blood pressure monitoring system

ABSTRACT

A sensor having a sensing surface for sensing blood pressure within an underlying artery of a patient includes a transducer, a sidewall, a flexible diaphragm and a fluid coupling medium. The sidewall is distinct from transducer and supports the transducer above the underlying artery. The fluid coupling medium is coupled between the sensing surface of transducer and the flexible diaphragm and transmits blood pressure pulses within the underlying artery from the flexible diaphragm to the sensing surface of transducer. In one embodiment, the fluid coupling medium is isolated from sidewall.

BACKGROUND OF THE INVENTION

The present invention relates to systems for measuring arterial bloodpressure. In particular, the invention relates to a sensor assembly formeasuring arterial blood pressure in a relatively continuous andnon-invasive manner.

Blood pressure has been typically measured by one of four basic methods:invasive, oscillometric, auscultatory and tonometric. The invasivemethod, otherwise known as an medal line (A-Line), involves insertion ofa needle into the artery. A transducer connected by a fluid column isused to determine exact arterial pressure. With proper instrumentation,systolic, mean and diastolic pressure may be determined. This method isdifficult to set up, is expensive and involves medical risks. Set up ofthe invasive or A-line method poses problems. Resonance often occurs andcauses significant errors. Also, if a blood clot forms on the end of thecatheter, or the end of the catheter is located against the arterialwall, a large error may result. To eliminate or reduce these errors, theset up must be adjusted frequently. A skilled medical practitioner isrequired to insert the needle into the artery. This contributes to theexpense of this method. Medical complications are also possible, such asinfection or nerve damage.

The other methods of measuring blood pressure are non-invasive. Theoscillometric method measures the amplitude of pressure oscillations inan inflated cuff. The cuff is placed against a cooperating artery of thepatient and thereafter pressurized to different levels. Mean pressure isdetermined by sweeping the cuff pressure and determining the mean cuffpressure at the instant the peak amplitude occurs. Systolic anddiastolic pressure is determined by cuff pressure when the pressureoscillation is at some predetermined ratio of peak amplitude.

The auscultatory method also involves inflation of a cuff placed arounda cooperating artery of the patient. Upon inflation of the cuff, thecuff is permitted to deflate. Systolic pressure is indicated whenKorotkoff sounds begin to occur as the cuff is deflated. Diastolicpressure is indicated when the Korotkoff sounds become muffled ordisappear. The auscultatory method can only be used to determinesystolic and diastolic pressures.

Because both the oscillometric and the auscultatory methods requireinflation of a cuff, performing frequent measurements is difficult. Thefrequency of measurement is limited by the time required to comfortablyinflate the cuff and the time required to deflate the cuff asmeasurements are made. Because the cuff is inflated around a relativelylarge area surrounding the artery, inflation and deflation of the cuffis uncomfortable to the patient. As a result, the oscillometric and theauscultatory methods are not suitable for long periods of repetitiveuse.

Both the oscillometric and auscultatory methods lack accuracy andconsistency for determining systolic and diastolic pressure values. Theoscillometric method applies an arbitrary ratio to determine systolicand diastolic pressure Values. Similarly, the auscultatory methodrequires a judgment to be made as to when the Korotkoff sounds start andwhen they stop. This detection is made when the Korotkoff sound is atits very lowest. As a result, the auscultatory method is subject toinaccuracies due to low signal-to-noise ratio.

The fourth method used to determine arterial blood pressure has beentonometry. The tonometric method typically involves a transducerincluding an array of pressure sensitive elements positioned over asuperficial artery. Hold down forces are applied to the transducer so asto flatten the wall of the underlying artery without occluding theartery. The pressure sensitive elements in the array typically have atleast one dimension smaller than the lumen of the underlying artery inwhich blood pressure is measured. The transducer is positioned such thatat least one of the individual pressure sensitive elements is over atleast a portion of the underlying artery. The output from one of thepressure sensitive elements is selected for monitoring blood pressure.The pressure measured by the selected pressure sensitive element isdependent upon the hold down pressure used to press the transduceragainst the skin of the patient. These tonometric systems measure areference pressure directly from the wrist and correlate this witharterial pressure. However, if a patient moves, recalibration of thetonometric system is required because the system may experience a changein gains. Because the accuracy of these tonometric systems depends uponthe accurate positioning of the individual pressure sensitive elementover the underlying artery, placement of the transducer is critical.Consequently, placement of the transducer with these tonometric systemsis time-consuming and prone to error.

The oscillometric, auscultatory and tonometric methods measure anddetect blood pressure by sensing force or displacement caused by bloodpressure pulses as the underlying artery is compressed or flattened. Theblood pressure is sensed by measuring forces exerted by blood pressurepulses in a direction perpendicular to the underlying artery. However,with these methods, the blood pressure pulse also exerts forces parallelto the underlying artery as the blood pressure pulses cross the edges ofthe sensor which is pressed against the skin overlying the underlyingartery of the patient. In particular, with the oscillometric and theauscultatory methods, parallel forces are exerted on the edges or sidesof the cuff. With the tonometric method, parallel forces are exerted onthe edges of the transducer. These parallel forces exerted upon thesensor by the blood pressure pulses create a pressure gradient acrossthe pressure sensitive elements. This uneven pressure gradient createsat least two different pressures, one pressure at the edge of thepressure sensitive element and a second pressure directly beneath thepressure sensitive element. As a result, the oscillometric, auscultatoryand tonometric methods produce inaccurate and inconsistent bloodpressure measurements.

SUMMARY OF THE INVENTION

A sensor having a sensing surface for sensing blood pressure within anunderlying artery of a patient includes a transducer, a compressiblesidewall, a flexible diaphragm and a fluid coupling medium. The sidewallis distinct from the transducer and supports the transducer above theunderlying artery. The flexible diaphragm is spaced from the sensingsurface of the transducer. The fluid coupling medium is coupled betweenthe sensing surface of the transducer and the flexible diaphragm andtransmits blood pressure pulses within the underlying artery from theflexible diaphragm to the sensing surface of the transducer. In oneembodiment, the fluid coupling medium is isolated from the sidewall sothat forces are not transmitted from the sidewall through the fluidcoupling medium to the transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective view of a blood pressure monitoring system having asensor assembly mounted to the wrist of a patient.

FIG. 2 block diagram of the blood pressure monitoring system of FIG. 1.

FIG. 3 a cross-sectional view of the sensor assembly of FIG. 1 mountedto the wrist of the patient.

FIG. 4 a cross-sectional view of the sensor assembly of FIG. 1 having asensor.

FIG. 5 is a cross-sectional view of an alternate embodiment of thesensor of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a blood pressure monitoring system 10 for measuring anddisplaying blood pressure within an underlying artery (not shown) withinwrist 12 of a patient. Monitoring system 10 includes wrist assembly 13,sensor assembly 14, cable 15 and monitor 16.

Wrist assembly 13 includes sensor support 18 and strap 20. Sensorsupport 18 fits over wrist 12 above an underlying artery (not shown) andsupports sensor assembly 14 over the underlying artery. Sensor support18 is preferably rigid.

Strap 20 comprises a flexible band and is preferably made of nylon.Strap 20 latches to sensor support 18 and wraps around wrist 12 tomaintain sensor assembly 14 on wrist 12.

Sensor assembly 14 is electrically coupled to monitor 16 through cable15 and generally includes motor assembly 22 and sensor 24. Motorassembly 22 is coupled to sensor support 18 and is mechanically coupledto sensor 24. Motor assembly 22 applies a variable hold down pressure tosensor 24 so that blood pressure can be sensed and measured as varyinghold down pressures are applied to the underlying artery by sensorassembly 14.

Sensor 24 is coupled to motor assembly 22. When placed on wrist 12,sensor 24 is positioned over the underlying artery. Sensor 24 senses andmeasures blood pressure pulses within the underlying artery.

Monitor 16 is coupled to motor assembly 22 and to sensor 24 by cable 15.Monitor 16 includes control switches or various inputs 25a-25h, digitaldisplays 26a-26c, and display screen 28. Inputs 25a-25h control monitor16 and permit monitor 16 to be calibrated. Inputs 25a-25c comprise hardkeys for controlling monitor 16. Inputs 25d-25h consist of softwareprogrammable keys which are adaptable for various functions. Digitaldisplays 26a-26c continually display systolic, diastolic and mean bloodpressure, respectively. Display screen 28 displays the blood pressurepulse, waveforms and prompts to guide the operator. Monitor 16 receivesthe sensed blood pressure pulse signals taken by sensor 24 andcalculates the systolic, diastolic and mean blood pressures. Once thesevalues are determined, monitor 16 displays the corresponding values inboth analog and digital form. Monitor 16 also controls motor assembly22.

In operation, sensor 24 is strapped to wrist 12 over the radial artery.Motor assembly 22 moves sensor 24 to vary the pressure applied to wrist12 above the radial artery. As this pressure is varied, an arterialpressure waveform is sensed. An arterial pressure waveform or shape isobtained by measuring amplitude of pressure versus time of an individualcardiac cycle. The shape of the waveform is a function of the appliedpressure and is used by digital signal processing circuitry of monitor16 to calculate systolic, mean and diastolic pressure. The calculatedpressures are displayed by displays 26a-26c and display screen 28.

FIG. 2 shows a block diagram of blood pressure monitoring system 10. Asbest shown by FIG. 2, monitor 16 further includes input signal processor30, analog-to-digital converter 32, microprocessor 34, inputs 25a-25h,motor drive 38, displays 26a-26c and 28, and power supply 42. Inoperation, microprocessor 34 receives inputted signals from inputs25a-25h. Inputs 25a-25h may also consist of a keyboard or other inputmechanisms. Inputs 25a-25h permit microprocessor 34 to be calibrated.

Microprocessor 34 controls motor drive 38 to vary hold down pressureapplied by motor assembly 22 on sensor 24. Hold down pressure is appliedto the anatomy of the patient directly above the artery by sensor 24.The hold down pressure applied by motor assembly 22 on sensor 24 isincreased over time. As the force or hold down pressure applied bysensor 24 increases, the amplitude of the blood pressure pulse alsoincreases until a maximum amplitude results. Once the maximum amplitudeor maximum energy transfer results, the amplitude of the blood pressurepulse begins to decrease as the artery begins to flatten out beyond thepoint of maximum energy transfer.

Sensor 24 senses and detects the amplitude and shape of the bloodpressure pulses within the underlying artery. Sensor 24 creates electricsensor signals representing the amplitude of the sensed blood pressurepulses. The sensor signals are transmitted to input signal processor 30of monitor 16. Input signal processor 30 processes the sensor signalsand filters any unwanted or undesirable noise and other effects. Thesensor signals are then transmitted from input signal processor 30 toanalog-to-digital convertor 32. Analog-to-digital convertor 32 convertsthe sensor signal into digital form. A digital signal representing theamplitude of the sensed blood pressure pulses is sent to microprocessor34.

Based upon the digital sensor signals representing the sensed amplitudeand shape of the blood pressure pulses, microprocessor 34 determineswave shape information by measuring amplitude and shape versus time ofindividual cardiac cycles. The arterial wave shape information isdetermined by sampling the arterial waves at a rate significantly aboveheart rate so that a good definition of the arterial pressure wave ismeasured. From this information, microprocessor 34 calculates systolic,diastolic and mean blood pressures. When no pressure gradient existsacross the face of sensor 24, the hold down pressure corresponding tothe cardiac cycle having the peak pressure amplitude or the maximumenergy transfer is substantially equal to the mean arterial pressure.Based upon the mean arterial pressure, microprocessor 34 calculatessystolic and diastolic blood pressure.

In the alternative, microprocessor 34 calculates blood pressure from therelationship between the pressure amplitude of the individual cardiacwaveform and the applied hold down pressure of sensor 24. These resultsmay be derived from waveforms both before and after the waveform thathas maximum energy transfer.

In addition, microprocessor 34 may also calculate blood pressure fromthe shape of individual cardiac waveforms. These results are based onthe area under part of the waveforms or they may be based on the shapeof a rise time on any number of parameters. The calculated bloodpressures are displayed on displays 26a-26c. Power supply 42 providespower to monitor 16 and motor assembly 22.

FIG. 3 is a cross-sectional view, taken along lines 3--3 of FIG. 1,showing wrist assembly 13 and sensor assembly 14 placed upon wrist 12 ofa patient having an underlying artery 44. FIG. 3 shows sensor support 18and strap 20 of wrist assembly 13 and sensor 24 of sensor assembly 14 ingreater detail. Sensor support 18 includes frame 46, spacer 48, latch50, stabilizing support 52 and screw 54. Frame 46 is a metal frame bentto partially surround wrist 12. Frame 46 includes lower strap holes 56a,56b and adjustment slot 58. Strap holes 56a, 56b are located along thelower end of frame 46. Strap hole 56b permits end loop 20a of strap 20to be secured to frame 46. Strap 20 is fed through strap hole 56a sothat strap 20 is doubled back, and free end 20b is attached to latch 50.Adjustment slot 58 extends upward from above strap hole 56b toward a topend of frame 46. Adjustment slot 58 permits stabilizing support 52 to bemoved up and down within slot 58 so that stabilizing support 52 may beadjusted for the particular anatomy to which sensor assembly 14 is beingsecured. Frame 46 supports motor assembly 22 and sensor 24 aboveunderlying artery 44 of wrist 12. Frame 46 also supports strap 20 belowwrist 12. As a result, sensor 24 is held in a stable position withrespect to wrist 12 while blood pressure pulses are being sensed andmeasured.

Spacer 48 is mounted along a top horizontal portion of frame 46 and ispositioned between sensor assembly 14 and frame 46. Spacer 48 spacessensor assembly 14 from frame 46.

Latch 50 is fixedly coupled to frame 46 between strap hole 56b andadjustment slot 58. Latch 50 releasably secures free end 20b of strap 20to frame 46 so that wrist 12 is supported and positioned between frame46, sensor 24 and strap 20.

Stabilizing support 52 generally consists of a V-shaped bar having afirst leg 52a extending parallel to adjustment slot 58 of frame 46 andhaving a second leg 52b extending over and above wrist 12. Stabilizingsupport 52 is slidably secured to frame 46 by screw 54. Screw 54 extendsthrough first leg 52a and adjustment slot 58. Screw 54 and slot 58cooperate to permit stabilizing support 52 to be vertically positionedwith respect to wrist 12. Thus, second leg 52b of stabilizing support 52holds wrist 12 down against strap 20 to limit movement of wrist 12 whileblood pressure pulses within underlying artery 44 are being sensed andmeasured.

Strap 20 consists of an elongate flexible band. Strap 20 has a first endlooped through strap hole 56b and secured to itself to form end loop20a. Strap 20 has second free end 20b which is fed through strap hole56a and doubled back below wrist 12 to latch 50 where free end 20b islatched and releasably secured to frame 46 by latch 50. Strap 20supports wrist 12 in position below frame 46 and sensor 24.

Also as best shown by FIG. 3, sensor 24 is coupled to cable 15 andincludes pivot block pin 62, pivot block 64, transducer 66, flange 68,sidewall 70, restraining ring 72, diaphragm 74, pressure or fluidcoupling medium 76 and fluid gel port 78. Pivot block pin 62 has a firstend coupled to pivot block 64 and a second end which is coupled to motorassembly 22. Pivot block pin 62 couples sensor 24 to motor assembly 22.

Pivot block 64 receives the first end of pivot block pin 62. Pivot block64 has a lower end which is coupled to transducer 66. Pivot block 64couples sensor 24 to motor assembly 22.

Transducer 66 is disc-shaped. Transducer 66 is coupled between pivotblock 64 and flange 68. Transducer 66 contains a pressure-sensitiveelement such as a piezoresistive sensor bridge (not shown) for sensingblood pressure pulses within artery 44.

Flange 68 is annular and is slightly concave so that sensor 24 betterconforms to the anatomy or shape of wrist 12. Flange 68 is fixedlycoupled around an outer perimeter of transducer 66. Flange 68 supportsside wall 70 and couples side wall 70 to transducer 66.

Side wall 70 is ring shaped and compressible, and is coupled to a lowersurface of flange 68. Side wall 70 is distant from transducer sensingelements (not shown) of transducer 66, yet engages tissue surroundingartery 44 to support transducer 66 above artery 44 and above tissuesurrounding artery 44. As a result, the exact positioning of transducer66 over artery 44 is not required. At the same time, side wall 70 is notso distant from transducer 66 so as to surround a large enough area oftissue surrounding artery 44 to cause discomfort to the patient. Becausesidewall 70 separates transducer 66 from the tissue surrounding artery44, blood pressure measurement errors caused by inadvertent patientmovement are lessened.

In addition, sidewall 70 creates a substantially zero pressure gradientacross sensor 24 so that sensor 24 more accurately measures bloodpressure. Sidewall 70 is constrained from expanding outward in a planardirection away from the outer perimeter of transducer 66. Because sidewall 70 is compressible, side wall 70 dampens and absorbs forces orpressure exerted by blood pressure pulses as the pulses cross side wall70 along the perimeter or edge of sensor 24. Side wall 70 also appliesforce to tissue surrounding artery 44. The force applied by side wall 70substantially equals force exerted by the tissue surrounding artery 44to offset or neutralize the force exerted from the tissue. As a result,the force applied by side wall 70 presses the tissue to a neutralposition so the pressure of artery 44 can be more accurately measured.The force of side wall 70 that is applied to the tissue surroundingartery 44 is coupled to flange 68. Flange 68 is coupled to transducer66, but is not coupled to transducer sensing elements (not shown) oftransducer 66. Thus, the force applied by side wall 70 which is used topress the tissue to a neutral position is not sensed by the transducersensing elements of transducer 66. This neutralizing effect of sensor 24allows blood pressure monitoring system 10 to more accurately measurethe arterial pressure of artery 44 without inaccuracies introduced byforces from the surrounding tissue. Consequently, side wall 70 reducesor eliminates uneven pressure gradients within fluid coupling medium 76across sensor 24 to create a substantially zero pressure gradient acrosssensor 24. As a result, sensor 24 more consistently and more accuratelymeasures blood pressure. Preferably, side wall 70 is formed from closedcell foam. Alternatively, side wall 70 may be formed from open cell foamor other compressible materials or structural designs.

Because side wall 70 is compressible and flexible, side wall 70 betterconforms to the anatomy or shape of wrist 12 without pinching off theunderlying artery as the sensor is pressed against the anatomy of thepatient. However, because side wall 70 is constrained from expandingoutward, side wall 70 does not stretch diaphragm 74 when being pressedagainst wrist 12. By preventing tension across diaphragm 74, sensor 24further eliminates pressure gradients across transducer 66, whichresults in more accurate and consistent blood pressure readings.

Restraining ring 72 normally consists of a flexible ring made of fiberor other similar material. Restraining dug 72 encircles side wall 70 andfurther prevents side wall 70 from expanding outward in a direction awayfrom the outer perimeter of transducer 66.

Diaphragm 74 is preferably formed from a thin flexible polymer orrubber. Diaphragm 74 extends across side wall 70 to form chamber 79 infront of transducer 66. Diaphragm 74 is preferably positioned acrossside wall 70 so as to be free of tension. Diaphragm 74 transmits bloodpressure pulses from a first side 80 to a second side 82 within chamber79.

Fluid coupling medium 76 preferably is a gel, although fluid couplingmedium 76 may consist of any fluid or liquid capable of transmittingpressure from diaphragm 74 to transducer 66. Fluid coupling medium 76 iscontained within chamber 79 between diaphragm 74, side wall 70, flange68 and transducer 66. Fluid coupling medium 76 interfaces betweendiaphragm 74 and transducer 66 and transmits the blood pressure pulsesfrom surface 82 of diaphragm 74 to transducer 66.

Sensor 24 continuously and accurately senses blood pressure pulseswithin the underlying artery. Because sidewall 70 is compressible,sensor 24 dampens forces parallel to the underlying artery which areextended upon sensor 24 by blood pressure pulses crossing beneath theedge of sensor 24. In addition, sensor 24 better conforms to the anatomyof wrist 12. Because sidewall 70 and diaphragm 74 are constrained fromexpanding outward and are free of tension, pressure gradients acrosstransducer 66 are eliminated. Moreover, sensor 24 also neutralizes thetissue surrounding artery 44. Consequently, more accurate and consistentblood pressure readings are taken. Moreover, sidewall 70, diaphragm 74and fluid coupling medium 76 form a large sensing area through whichblood pressure pulses may be transmitted to transducer 66. As a result,sensor 24 is not as dependent upon accurate positioning of transducer 66over the underlying artery. Sensor 24 quickly and accurately provides acontinuous measurement of blood pressure over long periods of usewithout discomfort to the patient.

Fluid port 78 extends into flange 68 and communicates with chamber 79.Port 78 permits chamber 79 to be filled with fluid coupling medium 76.

Cable 15 electrically couples sensor 24 to the monitor 16. Cable 15includes transducer leads 83, ground wire 84, connector 86, cable 88 andclamp 90. Transducer leads 83 consist of wires electrically coupled totransducer 66. Transducer leads 83 transmit signals representing thesensed blood pressure pulses from transducer 66.

Grounding wire 84 consists of a wire having a grounding clip 92 at oneend. Grounding clip 92 mounts onto fluid port 78. An opposite end ofgrounding wire 84 is electrically coupled to cable 88. Grounding wire 84electrically grounds sensor assembly 24.

Connector 86 electrically couples transducer leads 83 to cable 88. Cable88 has first end coupled to connector 88 and a second end which iscoupled to monitor 16 (shown in FIG. 1). Cable 88 permits sensor 24 totransmit signals representing the sensed blood pressure pulses tomonitor 16 where the signals are measured. Clamp 90 couples cable 88 toframe 46 of sensor support 18 and relieves strain within cable 88.

FIG. 4 is a cross-sectional view of sensor assembly 14 and sensorsupport 18 of wrist assembly 13 taken along lines 4--4 of FIG. 1. FIG. 4shows sensor 24 and motor assembly 22 in greater detail. Portions ofsensor support 18 are omitted for clarity. FIG. 4 best shows pivot blockpin 62 and pivot block 64 of sensor 24. As shown in FIG. 4, upper end62a of pivot block pin 62 is bifurcated and is frictionally coupled tomotor assembly 22. Because pivot block pin 62 is bifurcated, thediameter of pivot block pin 62 may be enlarged or reduced. As a result,pivot block pin 62 and sensor 24 may be removed from motor assembly 22without the use of tools by compressing pivot block pin 62 to reduce itsdiameter. Pivot block 64 includes a cavity for receiving the lower end62b of pivot block pin 62. Pivot block 64 rotates or pivots about lowerend 62b of pivot block pin 62 to permit accurate orientation of sensor24.

As best shown by FIG. 4, transducer 66 is generally disc-shaped andincludes transducer holder 94 and transducer element 96. Transducerholder 94 includes central bore 98 extending into a lower end oftransducer holder 94. Transducer holder 94 has a top end which iscoupled to pivot block 64. The lower end of transducer holder 94 isfixedly secured to flange 68. Transducer element 96 is supported andmounted within bore 98 of transducer holder 94.

Transducer element 96 is well known in the art and includes sensingsurface 100. Sensing surface 100 is preferably sensitive to pressurechanges within chamber 79 transmitted through fluid coupling medium 76.Transducer element 96 is positioned within bore 98 of transducer holder94 so that sensing surface 100 of transducer element 96 faces downwardout of bore 98. Transducer element 96 preferably comprises apiezoresistive sensor bridge. Transducer element 96 senses bloodpressure pulses from an underlying artery of a patient.

Motor assembly 22 presses sensor 24 against skin overlying theunderlying artery so that the amplitudes of blood pressure pulses may besensed over a range of various hold down pressures. As best shown byFIG. 4, motor assembly 22 includes base plate 106, outer sleeve 108,upper and lower outer races 110a and 110b, beating balls 112a and 112b,upper and lower inner races 114a and 114b, inner sleeve 116, threadedscrew shaft 118, stop arm 120, stop shaft 122, drive pulley 124, motor126, drive shaft 128, motor pulley 130, drive belt 132, ball 134 andsocket 136.

Base plate 106 is an elongate flat rigid plate which includes sleevehole 138, stop shaft hole 140 and drive shaft hole 142. Sleeve hole 138has a diameter large enough to permit outer sleeve 108, inner sleeve 116and screw shaft 118 to extend through sleeve hole 138. Stop shaft hole140 has a diameter large enough to permit stop shaft 122 to extendthrough stop shaft hole 140. Drive shaft hole 142 permits drive shaft128 to couple motor 126 to motor pulley 130.

Outer sleeve 108 is generally cylindrical and includes bore 144, upperinside shoulder 146, lower inside shoulder 148, and lower outsideshoulder 150. Bore 144 extends through outer sleeve 108. Towards a topend and a bottom end of outer sleeve 108, bore 144 widens to form upperinside shoulder 146 and lower inside shoulder 148, respectively. Towarda lower end of outer sleeve 108, an outer diameter of sleeve 108 narrowsto form lower outside shoulder 150. Lower outside shoulder 150 engagessleeve hole 138 of base plate 106 and fixedly couples outer sleeve 108to base plate 106. Upper inside shoulder 146 and lower inside shoulder148 support outer races 110. Inside races 114 are coupled to innersleeve 116. Inner races 110 and outer races 114 cooperate to support anannular array of bearing balls 112 therebetween. As a result, outersleeve 108 rotatably supports inner sleeve 116.

Inner sleeve 116 is cylindrical in shape and includes upper outsideshoulder 152, lower outside shoulder 154 and threaded inner bore 156.Towards an upper end and a lower end of inner sleeve 116, an outerdiameter narrows to form upper outside shoulder 152 and lower outsideshoulder 154, respectively. Shoulders 152 and 154 support inner races114a and 114b, respectively. Threaded inner bore 156 extends throughinner sleeve 156 and receives threaded screw shaft 118.

Threaded screw shaft 118 extends through threaded bore 156 of innersleeve 116. The lower end of threaded screw shaft 118 receives an upperend of pivot block pin 62. Consequently, threaded screw shaft 118 iscoupled to and supports sensor 24. Threaded screw shaft 118 is furthercoupled to stop arm 120.

Stop arm 120 generally consists of an elongate arm having a first endfixedly coupled to a lower end of threaded screw shaft 118 and having asecond end fixedly coupled to a lower end of stop shaft 122. Stop shaft122 extends upward from stop arm 120 through stop shaft hole 140 of baseplate 106. Stop arm 120 and stop shaft 122 prevent threaded screw shaft118 from rotating. At the same, stop arm 120 and stop shaft 122 permitthreaded screw shaft 118 to move up and down. As a result, rotation ofinner sleeve 116 with respect to threaded screw shaft 118 causesthreaded screw shaft 118 to move up and down as the threads of threadedscrew shaft 118 engage the threads of inner sleeve 116. Because sensor24 is coupled to threaded screw shaft 118, movement of threaded screwshaft 118 up and down causes sensor 24 to vary pressure applied to skinabove the underlying artery. As pressure is varied, an arterial pressurewaveform is generated which is measured by transducer 66 of sensor 24.

Drive pulley 124 generally consists of a circular pulley. Drive pulley124 has a groove along its outer perimeter sized to accommodate drivebelt 132. Drive pulley 124 is fixedly scarred to a lower end of innersleeve 116 below base plate 106. Rotation of drive pulley 124 permitsinner sleeve 116 to be rotated so that threaded screw shaft 118 israised and lowered.

Motor 126 is fixedly coupled to base plate 106. Motor 126 drives driveshaft 128. Drive shaft 128 extends through drive shaft hole 142 and iscoupled to motor pulley 130 below base plate 106. Motor pulley 130 iscircular and has an outer groove along its perimeter sized toaccommodate drive belt 132. Drive belt 132 generally consists of a bandor belt. Drive belt 132 fits within the grooves of drive pulley 124 andmotor pulley 130. Drive belt 132 partially encircles drive pulley 124and motor pulley 130 to provide rotational communication between drivepulley 124 and motor pulley 130.

In operation, motor 126 rotates motor pulley 130, which in turn, rotatesdrive pulley 124 and inner sleeve 116. As a result, rotation of motorpulley 130 by motor 126 causes threaded screw shaft 118 to move up anddown depending upon the rotational direction of motor pulley 130 andinner sleeve 116. By raising and lowering screw shaft 118 and sensor 24,motor 126 controls and continuously varies the hold down pressureapplied to the skin above the underlying artery by sensor 24. Thisinteraction between sensor 24 and the underlying artery permits bloodpressure monitoring system 10 to better measure blood pressure.

Ball 134 includes central bore 158 and convex surface 160. Central bore158 extends from a top end to a bottom end of ball 134. Central bore 158permits outer sleeve 108 to be press-fit within ball 134. Convex surface160 frictionally engages socket 136 to hold sensor assembly 14 inposition. Convex surface 160 of ball 134 also permits sensor assembly 14to be oriented in a proper position for accurate operation.

Socket 136 is generally rectangular and is coupled to frame 46 of sensorsupport 18. Socket 136 includes concave bore 162. Concave bore 162engages convex surface 160 of ball 134 to guide the positioning of ball134 within socket 136 so that sensor assembly 14 may be properlyoriented during operation.

Sensor 24 provides continuous external measurements of blood pressure inan underlying artery. Because sensor 24 calculates blood pressurenon-invasively, blood pressure is measured at a lower cost and withoutmedical risks. In addition, sensor 24 provides continuous measurementsof blood pressure. Because sensor 24 is relatively small compared to thelarger cuffs used with the oscillometric and auscultatory methods,sensor 24 applies a hold down pressure to only a relatively small areaabove the underlying artery of the patient. Consequently, blood pressuremeasurements may be token with less discomfort to the patient. Becausesensor 24 does not require inflation or deflation, continuous, morefrequent measurements may be taken. At the same time, sensor 24 permitsaccurate and consistent calculation of blood pressure. Because the sidewall, diaphragm and fluid coupling medium of sensor 24 forms a largesensing area through which blood pressure pulses may be transmitted totransducer 66, sensor 24 is not as dependent upon accurate positioningof transducer 66 over the underlying artery. Thus, sensor 24 is moretolerant to patient movement as measurements are being taken. Moreover,because the side wall of sensor 24 dampens and absorbs forces from theblood pressure pulses which are parallel to the underlying artery,uneven pressure gradients across transducer 66 are eliminated. The sidewall of sensor 24 also presses tissue surrounding the artery toneutralize or offset forces exerted by the tissue. Consequently, sensor24 senses blood pressure more consistently and more accurately.

FIG. 5 shows a cross-sectional view of an alternate embodiment (sensor180) to sensor 24 shown in FIG. 4. For sake of illustration, thoseelements of sensor 180 which are the same as those elements of sensor 24are numbered similarly. Sensor 180 includes transducer 66, flange 182,sidewall 184, diaphragm 186 and fluid coupling medium 188. As disusedabove, transducer 66 is mounted to pivot block pin 62 and includestransducer holder 94 and transducer element 96. Transducer holder 94 iscoupled to flange 182 and supports transducer element 96.

Transducer element 96 is well known in the art and includes sensingsurface 100. Sensing surface 100 is sensitive to pressure changestransmitted through fluid coupling medium 188. Transducer element 96preferably comprises a piezoresistive sensor bridge. Transducer element96 senses blood pressure pulses from an underlying artery of a patientand transmits the sensed blood pressure pulses through cable 15 tomonitor 16 (not shown) for measurement and analysis.

Flange 182 is coupled between transducer 66 and sidewall 184 andincludes plate 190, top 192, outer ring 194, upper insert 196 and lowerinsert 198. Plate 190 generally consists of a flat annular collar. Plate190 is fixedly secured around the lower portion of transducer holder 94of transducer 66. Plate 190 provides a supporting area for mountingtransducer 66 to top 192.

Top 192 is a generally flat annular platform, base or stand and includesdepression 200, bore 202, and shoulder 204. Depression 200 extends intoan upper surface of top 192 and preferably has a shape nearly identicalto the shape of plate 190. Depression 200 permits plate 190 andtransducer 66 to be securely fixed to and centered on top 192.

Bore 202 extends from a lower surface of top 192 to the upper surface oftop 192. Bore 202 is preferably coaxially centered about sensing surface100 of transducer element 96. Bore 202 has a diameter sized for thereception of upper insert 196.

Shoulder 204 is defined by outward extending ends extending along anouter perimeter of top 192 near the upper surface. Shoulder 204 and theouter perimeter of top 204 are sized for receiving and engaging outerring 194. Shoulder 196 limits accidental upward movement of outer ring194 and provides an additional surface for securely mounting outer ring194.

Outer ring 194 generally consists of a circular ring having an innerdiameter large enough to receive top 192 below shoulder 204. Ring 194engages the outer perimeter of top 192 below shoulder 204 to partiallysupport sidewall 184 captured therebetween. Outer ring 194 is preferablyfixed to top 192 and sidewall 184 by adhesive. Alternatively, outer ring194 may be press fit around top 192 and sidewall 184.

Upper insert 196 is a generally cylindrical shaped member including stepor spar 206 and bore 208. An outer surface or perimeter of insert 196projects outwardly to form spar 206. Spar 206 engages the lower surfaceof top 192 to partially support sidewall 184 which is partially capturedbetween top 192 and spar 206. In the preferred embodiment, adhesive isused between the lower surface of top 192 and spar 206 to fixedly securethe portion of sidewall 184 trapped therebetween. Alternatively, spar206 may be press fit against the lower surface of top 192 to secure andsupport sidewall 184. Spar 206 further divides the outer perimeter ofinsert 196 into two portions, an upper portion 210 and a lower portion212. Upper portion 210 fits within bore 202 of top 192. Upper portion210 preferably has a height approximately equal to the thickness of top192 between the lower surface of top 192 and depression 200 so thatinsert 196 engages the lower surface of transducer holder 94. Upperportion 210 is preferably adhesively secured to top 192 within bore 202.Lower portion 212 extends below spar 206. Lower portion 212, spar 206and sidewall 184 define expansion cavity 214. Expansion cavity 214enables diaphragm 186 to initially change shape while only experiencinga small change in volume.

Bore 208 extends through insert 196 and partially contains fluidcoupling medium 188. Bore 208 has a diameter sized for the reception oflower insert 198.

Lower insert 198 is a thin, elongated, annular ring including bore 216and lower lip 218. Bore 216 extends through lower insert 198 andpartially contains fluid coupling medium 188. Lip 218 projects outwardlyfrom a lower end of insert 198. Lower insert 198 fits within bore 208 ofupper insert 196 until lip 218 engages a lower rim of upper insert 196.Lower insert 198 is preferably adhesively affixed to upper insert 198.Alternatively, lower insert 198 may be press fit within upper insert196. Lip 218 of lower insert 196 engages upper insert 196 to supportdiaphragm 186 between lip 218 and insert 196.

Flange 182 serves as a base or supporting structure upon whichtransducer 66, sidewall 184 and diaphragm 186 are affixed. Because plate190, top 192, outer ring 194, upper insert 196, and lower insert 198 offlange 182 all engage and fit within one another to mount transducer 66,sidewall 184 and diaphragm 186, flange 182 permits sensor 180 to beeasily manufactured and assembled at a lower cost and in less time.

Sidewall 184 supports and spaces transducer 66 above the underlyingartery and includes top sidewall or ring 220 and bottom sidewall or ring222. Top ring 220 generally consists of annular compressible ringcoupled between top 192 of flange 182 and bottom ring 222. Ring 220 ispreferably formed from a generally circular sheet 221 of flexiblematerial, such as vinyl, and is partially filled with fluid 225. Sheet221 has a hole sized to fit around upper portion 210 of upper insert196. Sheet 221 includes outer edge portion 224 and inner edge portion226. Outer edge portion 224 is trapped and held between outer ring 194and top 192. Inner edge portion 226 is trapped and supported between top192 and spar 206 of upper insert 196. As a result, ring 220 forms acontinuous annular chamber which is partially filled with fluid 225.Because ring 220 is formed from a flexible material and is onlypartially filled with fluid 225, top ring 220 is compressible so as tobe able to conform to the anatomy of the patient surrounding theunderlying artery. As a result, the distance between top 192 and thepatient's anatomy can vary around the periphery of sidewall 184according to the contour of the patient's anatomy. Furthermore, becausefluid 225 is permitted to flow through and around ring 220, pressurearound ring 220 is equalized around the patient's anatomy.

Bottom sidewall or ring 222 generally consists of an annularcompressible and flexible ring and is preferably formed from a foamrubber or other pulse dampening material such as open celled foam orclosed cell foam. Ring 222 is centered about and positioned between topring 220 and diaphragm 186. Ring 222 is isolated from fluid couplingmedium 188. Because ring 222 is formed from a compressible material,ring 222 absorbs and dampens forces in a direction parallel to theunderlying artery which are exerted by the blood pressure pulses onsensor 180 as the blood pressure pulse crosses sensor 180. Becausebottom ring 222 is isolated from fluid coupling medium 188, the forcesabsorbed or received by ring 222 cannot be transmitted to the fluidcoupling medium 188. Instead, these forces are transmitted across ring222 and ring 220 to top 192. Because this path is distinct and separatefrom fluid coupling medium 188, fluid coupling medium 188 is isolatedfrom these forces. In addition, bottom ring 222 also presses tissuesurrounding the artery to neutralize or offset forces exerted by thetissue. As can be appreciated, bottom ring 222 may alternativelypartially surround active portion 240.

Diaphragm 186 is a generally flat surfaced sac preferably formed fromupper diaphragm sheet 230 and lower diaphragm sheet 232. Upper diaphragmsheet 230 is an annular sheet of flexible material having an innerportion 234, an intermediate portion 235, an outer portion 236 and aninner diameter sized to fit around lower insert 198. Inner portion 234is trapped or captured between lip 218 of lower insert 198 and thebottom rim of upper insert 196 to support diaphragm 186 from flange 182.Inner portion 234 is preferably adhesively affixed between lip 218 andupper insert 196.

Intermediate portion 235 lies between inner portion 234 and outerportion 236. Intermediate portion 235 is adjacent to expansion cavity214 and is isolated from rings 220 and 222 of sidewall 184. Becauseintermediate portion 235 is positioned adjacent to expansion cavity 214,intermediate portion 235 is permitted to initially move upward intoexpansion cavity 214 as sidewall 184 and diaphragm 186 conform to theanatomy of the patient surrounding the underlying artery while thecavity containing fluid coupling medium 188 experiences only a smallchange in volume. As bottom ring 222 is pressed against the anatomy ofthe patient surrounding the artery to neutralize or offset forcesexerted by the tissue, diaphragm 186 is also compressed. However,because intermediate portion 235 is permitted to roll into expansioncavity 214, the cavity containing fluid coupling medium 188 does notexperience a large volume decrease and a large corresponding pressureincrease. Thus, sensor 180 permits greater force to be applied to theanatomy of the patient through sidewall 184 to neutralize tissuesurrounding the artery without causing a corresponding large change inpressure within the cavity containing fluid coupling medium 188 as theheight of sidewall 184 changes. As a result, sensor 180 achieves moreconsistant and accurate blood pressure measurements.

Outer portion 236 is the outer most edge of upper diaphragm sheet 230.Outer portion 236 extends within and outwardly beyond ring 222 ofsidewall 184. Outer portion 236 is preferably not bonded or coupled to alower surface of ring 222. Outer portion 236 of upper diaphragm sheet230 is bonded to lower diaphragm sheet 232 at a distance within theinner diameter of ring 222 of sidewall 184 so that intermediate portion235 does not contact ring 222 of sidewall 184. To further preventintermediate portion 235 from contacting ring 222, intermediate portion235 is preferably made of a flexible material having sufficient rigidityto prevent intermediate portion 235 from bowing outwardly and contactingring 222.

Lower diaphragm sheet 232 is a generally circular sheet of flexiblematerial capable of transmitting forces from an outer surface to aninner surface of sheet 232. Sheet 232 is coupled to upper diaphragmsheet 230 and is configured for being positioned over the anatomy of thepatient above the underlying artery. Lower diaphragm sheet 232 includesnon-active portion or skirt 238 and active portion 240. Skirt 238constitutes the area of sheet 232 where upper diaphragm sheet 230,namely outer portion 236, is bonded to lower diaphragm sheet 232.Because skirt 238 and outer portion 236 are generally two bonded sheetsof flexible material, forces parallel to the underlying artery aretransmitted across skirt 238 and outer portion 236 and are dampened bythe compressible material of ring 222. In addition, because skirt 238and outer portion 236 preferably extend outward beyond ring 222 ofsidewall 184 and are not fixedly secured to ring 222, skirt 238, outerportion 236 and active portion 240 are permitted to bow inwardly tobetter conform to the anatomy of the patient surrounding the underlyingartery.

Active portion 240 is constituted by the portion of lower diaphragmsheet 232 which is not bonded to upper diaphragm sheet 230. Activeportion 240 is positioned below and within the inner diameter of ring222 of sidewall 184. Active portion 240 of diaphragm 186 is the activearea of sensor 180 which receives and transmits pulse pressure totransducer 66. Active portion 240 of diaphragm 186, intermediate portion235 of upper diaphragm sheet 230, bore 216 of lower insert 198 and bore208 of upper insert 196 define interface chamber 242.

Interface chamber 242 is an elongated fluid passage or cavity extendingfrom active portion 240 of diaphragm 186 through bores 208 and 216 tosensing surface 100 of transducer element 96. Interface chamber 242 isisolated from sidewall 184. Interface chamber 242 contains fluidcoupling medium 188.

Fluid coupling medium 188 is preferably a gel, although fluid couplingmedium 188 may consist of any fluid or liquid capable of transmittingpressure from diaphragm 186 to transducer 66. Fluid coupling medium 188interfaces between active portion 240 of diaphragm 186 and transducer 66and transmits blood pressure pulses from active portion 240 to sensingsurface 100 of transducer element 96. Because fluid coupling medium 188is contained within interface chamber 242 which is isolated fromsidewall 184, fluid coupling medium 188 does not transmit blood pressurepulses parallel to the underlying artery, forces from the tissuesurrounding the underlying artery and other forces absorbed by sidewall184 to transducer 66. As a result, sensor 180 more accurately measuresand detects arterial blood pressure.

As with sensor 24, sensor 180 provides continuous external measurementsof blood pressure in an underlying artery. Because sensor 180 calculatesblood pressure non-invasively, blood pressure is measured at a lowercost and without medical fish. In addition, sensor 180 providescontinuous measurements of blood pressure. Because sensor 180 isrelatively small compared to the larger cuffs used with oscillometricand auscultatory methods, sensor 180 applies a hold down pressure toonly a relatively small area above the underlying artery of the patient.Consequently, blood pressure measurements may be taken with lessdiscomfort to the patient. Because sensor 180 does not require inflationor deflation, continuous, more frequent measurements may be taken.

Furthermore, sensor 180 better conforms to the anatomy of the patient soas to be more comfortable to the patient and so as to achieve moreconsistent and accurate blood pressure measurements. Because ring 220 iscompressible and is partially filled with fluid, FIG. 220 betterconforms to the anatomy of the patient and equalizes pressure appliedaround FIG. 220 to the patient's anatomy. Because bottom ring 222 iscompressible and because diaphragm 186 is flexible and is permitted tobow or deform inwardly, bottom ring 222 and diaphragm 186 also betterconform to the anatomy of the patient. At the same time, however, sensor180 does not experience a large sudden increase in pressure in interfacechamber 242 as bottom ring 222 and diaphragm 186 are pressed against theanatomy of the patient. Top ring 220 and bottom ring 222 apply force tothe anatomy of the patient to neutralize the forces exerted by tissuesurrounding the underlying artery. Because rings 220 and 222 are bothcompressible, the height of sidewall 184 decreases as sidewall 184 ispressed against the patient. As a result, diaphragm 186 is alsocompressed. However, because intermediate portion 235 of upper diaphragmsheet 230 is permitted to move upward into expansion cavity 214,interface chamber 242 partially defined by diaphragm 186 does notexperience a large volume decrease and a corresponding large pressureincrease. Thus, sidewall 184 is able to apply a greater force to theanatomy of the patient without causing a corresponding large, errorproducing increase in pressure within interface chamber 242 due to thechange in height of sidewall 184 and the change in shape of diaphragm186.

At the same time, sensor 180 permits accurate and consistent calculationof blood pressure. Because sidewall 184, diaphragm 186 and fluidcoupling medium 188 of sensor 180 form a large sensing area throughwhich blood pressure pulses may be transmitted to transducer 66, sensor180 is not as dependent upon accurate positioning of transducer 66 overthe underlying artery. Thus, sensor 180 is more tolerant to patientmovement as measurements are being taken.

Moreover, sensor 180 achieves a zero pressure gradient across the activeface or portion 240 of the sensor, achieves a zero pressure gradientbetween the transducer and the underlying artery, attenuates or dampenspressure pulses that are parallel to the sensing surface of the sensor,and neutralizes forces of the tissue surrounding the underlying artery.Sensor 180 contacts and applies force to the anatomy of the patientacross skirt 238 and active portion 240. However, the pressure withininterface chamber 242 is substantially equal to the pressure appliedacross active portion 240. The remaining force applied by sensor 180across skirt 238 which neutralizes or offsets forces exerted by thetissue surrounding the underlying artery is transferred through sidewall184 to top 192. As a result, the geometry and construction of sensor 180provides the proper ratio of pressures between skirt 238 and activeportion 240 to neutralize tissue surrounding the underlying artery andto accurately measure the blood pressure of the artery. In addition,because fluid coupling medium 188 within interface chamber 242 isisolated from sidewall 184, pressure pulses parallel to the underlyingartery, forces from tissue surrounding the underlying artery and otherforces absorbed by sidewall 184 are not transmitted through fluidcoupling medium 188 to transducer 66. Consequently, sensor 180 alsoachieves a zero pressure gradient between transducer 66 and theunderlying artery.

As can be appreciated, transducer 66 may alternatively be housed andspaced separate from flange 182, sidewall 184 and diaphragm 186. In suchan embodiment, interface chamber 242 extends from active portion 240through a conduit member such as a tube to the sensing surface 100 oftransducer element 96. Fluid coupling medium 188 within chamber 242transmits pressure from diaphragm 232 to the separately housedtransducer element 96.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A sensor for sensing blood pressure within anunderlying artery of a patient, the sensor comprising:a pressuretransducer for sensing blood pressure pulses of the underlying artery,the transducer having a sensing surface; a flexible diaphragm spacedfrom the sensing surface, wherein the flexible diaphragm at leastpartially defines an interface chamber in communication with the sensingsurface of the pressure transducer; a fluid coupling medium within theinterface chamber for transmitting blood pressure pulses within theunderlying artery from the flexible diaphragm to the sensing surface ofthe transducer; and a variable height, body conforming spacing structurefor spacing the transducer from the underlying artery, wherein thespacing structure defines an expansion cavity adjacent the flexiblediaphragm so that the interface chamber containing the fluid couplingmedium may undergo a change in shape without a corresponding change involume and pressure.
 2. A sensor for sensing blood pressure within anunderlying artery of a patient, the sensor comprising:a transducer forsensing blood pressure pulses of the underlying artery, the transducerhaving a sensing surface; a flexible diaphragm having an active portionfor transmitting blood pressure pulses of the underlying artery; a fluidcoupling medium coupled between the flexible diaphragm and the sensingsurface of the pressure transducer for transmitting the blood pressurepulses within the underlying artery from the flexible diaphragm to thesensing surface of the transducer; and a variable height sidewallisolated from the sensing surface of the transducer and the fluidcoupling medium for engaging tissue surrounding the underlying artery.3. A sensor for sensing blood pressure within an underlying artery of apatient, the sensor comprising:a pressure transducer for sensing bloodpressure pulses of the underlying artery, the transducer having asensing surface; a flexible diaphragm having an active portion fortransmitting blood pressure pulses of the underlying artery; interfacemeans coupled between the sensing surface of the transducer and theflexible diaphragm for transmitting the blood pressure pulses within theunderlying artery from the flexible diaphragm to the sensing surface ofthe transducer; and flexible, body conforming means isolated from theinterface means and at least partially surrounding the active portionfor conforming to an anatomy proximate the underlying artery.
 4. Asensor for sensing blood pressure within an underlying artery of apatient, the sensor comprising:a pressure transducer for sensing bloodpressure pulses of the underlying artery, the transducer having asensing surface; a flexible diaphragm having an active portion fortransmitting blood pressure pulses of the underlying artery; interfacemeans coupled between the sensing surface of the transducer and theflexible diaphragm for transmitting the blood pressure pulses within theunderlying artery from the flexible diaphragm to the sensing surface ofthe transducer; and means isolated from the interface means and at leastpartially surrounding the active portion for conforming to the anatomyproximate an underlying artery, and wherein the means for conformingincludes means for equalizing pressure at least partially around theactive portion.
 5. The sensor of claim 4 wherein the means forequalizing pressure includes a compressible member at least partiallysurrounding the active portion, the member having a top surface and abottom surface, the compressible member being partially filled with afluid so that the distance between the top surface and the bottomsurface varies along the compressible member to conform to the anatomyof the patient proximate the underlying artery.
 6. The sensor of claim 5including:a foam member at least partially surrounding the activeportion and positioned between the compressible member and the anatomyof the patient.
 7. A sensor for sensing blood pressure within anunderlying artery of a patient, the sensor comprising:a pressuretransducer for sensing blood pressure pulses of the underlying artery,the transducer having a sensing surface; a flexible diaphragm having anactive portion for transmitting blood pressure pulses of the underlyingartery; interface means coupled between the sensing surface of thetransducer and the flexible diaphragm for transmitting the bloodpressure pulses within the underlying artery from the flexible diaphragmto the sensing surface of the transducer; means isolated from theinterface means and at least partially surrounding the active portionfor conforming to the anatomy proximate an underlying artery, and fordampening forces in a direction parallel to the underlying artery whichare exerted by the blood pressure pulses on the sensor so that asubstantially zero pressure gradient exists within the interface meansacross the pressure transducer.
 8. The sensor of claim 7 wherein themeans for conforming and dampening includes a compressible sidewall atleast partially surrounding the active portion.
 9. A sensor for sensingblood pressure within an underlying artery of a patient, the sensorcomprising:a pressure transducer for sensing blood pressure pulses ofthe underlying artery, the transducer having a sensing surface: aflexible diaphragm having an active portion for transmitting bloodpressure pulses of the underlying artery; interface means coupledbetween the sensing surface of the transducer and the flexible diaphragmfor transmitting the blood pressure pulses within the underlying arteryfrom the flexible diaphragm to the sensing surface of the transducer;and means isolated from the interface means and at least partiallysurrounding the active portion for conforming to the anatomy proximatean underlying artery and at least partially surrounding the activeportion for neutralizing force exerted by the tissue proximate theunderlying artery as the underlying artery is compressed.
 10. The sensorof claim 9 wherein means for conforming and neutralizing includes acompressible sidewall at least partially surrounding the active portion.11. A sensor for measuring blood pressure pulses within an underlyingartery surrounded by tissue as the underlying artery is compressed,wherein tissue proximate the underlying artery exerts a force as theunderlying artery is compressed, the sensor comprising:a pressuretransducer for sensing blood pressure pulses of the underlying artery,the transducer having a sensing surface; a flexible diaphragm spacedfrom the sensing surface, the diaphragm having an active portion forreceiving forces exerted by the blood pressure pulses; interface meanscoupled between the sensing surface of the transducer and the flexiblediaphragm for transmitting the blood pressure pulses within theunderlying artery from the flexible diaphragm to the sensing surface ofthe transducer; and flexible, body conforming means isolated from theinterface means and at least partially surrounding the active portionfor neutralizing the force exerted by the tissue proximate theunderlying artery.
 12. A sensor for sensing blood pressure within anunderlying artery, the sensor comprising:a pressure transducer forsensing blood pressure pulses of the underlying artery, the transducerhaving a sensing surface; flexible, body conforming spacing means forspacing the transducer from the underlying artery; a flexible diaphragmspaced from the sensing surface; and interface means coupled between thesensing surface of the transducer and the flexible diaphragm fortransmitting the blood pressure pulses within the underlying artery fromthe flexible diaphragm to the sensing surface of the transducer, whereinthe interface means are isolated from the spacing means.
 13. The sensorof claim 12 wherein the interface means comprises a fluid couplingmedium and wherein the flexible diaphragm partially defines an interfacechamber extending between the flexible diaphragm and the sensing surfaceof the transducer, the interface chamber containing the fluid couplingmedium and being substantially isolated from the spacing means so as toprevent pressure from the spacing means from being transmitted to thefluid coupling medium and to the sensing surface of the transducer. 14.The sensor of claim 13 wherein the flexible diaphragm includes:a firstflexible member having an active portion at least partially encircled bythe spacing means, wherein the active portion receives forces exerted bythe blood pressure pulses; and a second flexible member supportedbetween the spacing means and the first flexible member and coupled tothe first flexible member, the second flexible member having a portionabove the active portion which is isolated from the spacing means sothat the isolated portion of the second flexible member and the activeportion of the first flexible member at least partially define theinterface chamber.
 15. A sensor for sensing blood pressure within anunderlying artery of a patient, the sensor comprising:a pressuretransducer for sensing blood pressure pulses of the underlying artery,the transducer having a sensing surface; a flexible diaphragm having anactive portion for transmitting blood pressure pulses of the underlyingartery; interface means coupled between the sensing surface of thetransducer and the flexible diaphragm for transmitting the bloodpressure pulses within the underlying artery from the flexible diaphragmto the sensing surface of the transducer; and a variable height sidewallisolated from the interface means for engaging tissue proximate theunderlying artery.
 16. A sensor for sensing blood pressure within anunderlying artery of a patient, the sensor comprising:a fluid filledsensing chamber having a diaphragm; a flexible body conforming sidewallisolated from the fluid filled sensing chamber; and a pressuretransducer fluidly coupled to the fluid filled sensing chamber.
 17. Asensor for sensing blood pressure within an underlying artery of apatient, the sensor comprising:a fluid filled sensing chamber having adiaphragm; a transducer fluidly coupled to the fluidly filled sensingchamber, wherein the transducer senses fluid pressure within thechamber; and a flexible body conformable wall proximate the sensingchamber and isolated from the sensing chamber for applying force to theartery while preventing pressure in a direction generally parallel tothe artery from being applied to the sensing chamber.
 18. A sensor forsensing blood pressure pulses within an underlying artery surrounded bytissue as the underlying artery is compressed, the sensor comprising:atransducer; a flexible diaphragm for placement above the underlyingartery; a fluid coupling medium between the transducer and the flexiblediaphragm, wherein the fluid coupling medium transmits blood pressurepulse signals from the underlying artery to the transducer; and aflexible, variable height, body conforming sidewall isolated from thefluid coupling medium and positioned for engaging tissue proximate tothe underlying artery.